strong
Explanation
The Joke
A person tells their companion "Oh, I was feeling so anxious today I could hardly breathe." The companion responds enthusiastically: "Wow! You're gonna have such a strong heart from all that exercise you're giving it." The caption below reads: "The fact that this isn't how it works is proof of God's hatred."
The Humor
The comic takes the common experience of anxiety — specifically the physical symptom of a racing heart and difficulty breathing — and applies the logic of physical exercise to it. If your heart is racing from anxiety the same way it races during a workout, shouldn't you get the same cardiovascular benefits? The companion's cheerful reframing of a panic attack as a free cardio session is absurdly optimistic.
The caption delivers the real punchline with mock-theological despair: the fact that anxiety gives you all the unpleasant sensations of vigorous exercise without any of the health benefits is framed as evidence of a malevolent (or at least spiteful) universe. It's a darkly funny observation that the human body seems specifically designed to make suffering as unproductive as possible.
Broader Context
SMBC often explores the cruel ironies of human biology and psychology. This comic fits into Weinersmith's recurring interest in how the human body seems poorly designed for the modern world — we get all the downsides of stress responses evolved for life-threatening situations, applied to situations like email notifications and social interactions.